1. Field of the Invention
The present invention relates to an isomerization process of tricycloalkane, applicable in a catalytic reaction with an ionic liquid having high activity and immiscible with reactants, and particularly applicable in isomerization of tricycloalkane such as endo-tetrahydrodicyclopentadiene (endo-THDCPD) and exo-tetrahydrodicyclopentadiene (exo-THDCPD) with an acidic ionic liquid of aluminum trichloride.
2. Related Art
Since many years ago, acidic catalysts have been applied in oil refining and petrochemical industries, including processes such as cracking, alkylation, isomerization, polymerization, etherification, esterification, acylation and transesterification. Traditional Lewis acid such as aluminum trichloride (AlCl3) and boron trifluoride (BF3) and Bronsted acid such as hydrofluoric acid (HF) and sulfuric acid (H2SO4) are used as catalyst and have effective catalytic activity, in most of alkylation and isomerization. However, some persistent difficulties are still in existence, for example, problems existed in product separation, catalyst recovery, equipment corrosion, treatment of acidic waste water and massive spent catalyst. Therefore, both industrial and academic circles have actively endeavored to research them, with expectation to develop a solid strong acid or superacid catalyst to replace the traditional liquid acids in the processes.
One improved process is to directly load anhydrous aluminum trichloride (AlCl3) onto a support of inorganic material, to prepare a loaded Lewis acid, which has good reaction activity and selectivity in, for example, catalytic cracking of hydrocarbons, isomerization of aromatic hydrocarbons, and alkylation, and also improve the disadvantages above. In addition, montmorrilonite, polymer, and molecular sieve are also used as support to prepare loaded aluminum trichloride (AlCl3) catalysts, all of which can exhibit good activity and selectivity. Commercial applications thereof are supposed to be broadened if breakthroughs in selection of support, loading technology, and regeneration process can be achieved in future.
Solid acids have disadvantages while being convenient in application, for example, difficulty in contact with reactants. Furthermore, because aluminum trichloride (AlCl3) reacts with hydroxyl (—OH) on a surface of its support and leads to a species containing —O—AlCl2 group, acidity is lowered, and activity decline is easily caused by carbon accumulation because of high reaction temperature.
Therefore, use of an acidic ionic liquid is another preferred selection, in that its properties, such as acidity and solubility, can be optionally adjusted, and reactants and reaction products can be easily separated from the ionic liquid catalyst, i.e. they are in an immiscible liquid-liquid biphasic system.
The ionic liquid will gradually play an important role in catalytic process in future green chemistry industry, since it has no vapor pressure, can be adjusted for acidity and solubility by cation and anion species and their molar ratios to aluminum trichloride, and thus can perform a catalytic reaction effectively.